2cups(280 g) Kim's gluten free flour blend(you can substitute Cup4Cup or any other general GF flour blend with xanthan gum)
2cups(400 g) granulated sugar
6tbsp(53 g) gluten free flour blend
1cup(240 ml) fresh lemon juice
powdered sugar for dusting
For the Shortbread Crust:
Preheat the oven to 325° F. Line a 9 by 13-inch baking pan with parchment paper with some overhang so you can easily lift the bars out of the pan.
In a large bowl, mix together butter, sugar, vanilla, salt, and flour blend. Press into prepared pan and bake for 23-25 minutes, or until set and very lightly browned around the edges. Remove from the oven and carefully prick the shortbread with a fork just on the top (don't let it go through all the way to the bottom). Set aside while you prepare the filling.
For the Filling:
Combine the sugar and flour in a large bowl and whisk thoroughly. Add the eggs, followed by the lemon juice and continue whisking until completely combined.
Pour this mixture over the warm crust and bake for another 26-28 minutes, or until set and the filling doesn't jiggle when the pan is lightly shaken.
Cool completely at room temperature. For neat slices, refrigerate for at least an hour. Sprinkle with powdered sugar and cut into small squares. Store in the refrigerator for up to one week, or bars can be frozen, wrapped individually, for 3-4 months.